This invention relates to a method of making electrolytic metal foil and an apparatus used therefor. More particularly, it is concerned with a method that can make metal foil of good quality, particularly an electrolytic copper foil for a printed circuit, in a high current density and high electric power efficiency, which foil is of dense quality and excellent physical properties and has a roughened surface with minute and uniform irregularities, and further can substantially perfectly prevent equipments or atmospheres from being contaminated owing to the splashing of an electrolytic solution or the generation of mist during the electrolytic making, and resulting foil from being lowered in quality, and also concerned with an apparatus used for making the same.
Of the electrolytic metal foil, nowadays produced in greatest quantities is electrolytic copper foil for printed circuits. Almost all of this electrolytic copper foil are produced in a continuous process according to the method as described below.
Namely, it has been practiced to horizontaly support a drum whose surface is comprised of stainless steel, titanium or a chromium coating and dipping it in part in an electrolytic solution comprising, for example, copper sulfate and sulfate; cause a direct current to flow between an opposite electrode provided in face of the surface of the drum in the solution, having a surface of, for example, copper, lead, platinum or a platinum group oxide, and the drum surface serving as a cathode; rotate the drum while controlling the intensity of the electric current and the rotational speed so that the electrodeposited copper may come out from the solution in the air exactly when it was built up to a desired thickness; strip off the electrodeposited copper layer from the drum; and then winding it up.
What is required for continuing the electrolytic treatment and producing electrolytic copper foil of good quality is that the electrolytic solution held between the both electrodes is circulated, agitated and refreshed, and a variety of methods and apparatus have been hitherto proposed for such purposes.
For example, the apparatus disclosed in U.S. Pat. No. 1,978,037 is of the type in which anodes provided in face of a cathode drum in an electrolytic tank are divided right and left into two portions to have a gap therebetween, wherein, once the electrolysis is effected, the electrolytic solution held between the both electrodes rises along with a rise of generated gas until it overflows from an upper end of the anodes, and the electrolytic solution in the electrolytic tank is sucked up from the gap between the anodes at the central lower part to the space defined between the both electrodes, so that the electrolytic solution between the both electrodes can be refreshed in this manner.
U.S. Pat. No. 1,952,762 also discloses a type in which three gaps are provided between the above anodes.
U.S. Pat. No. 2,044,415 further discloses an apparatus in which a pipe for ejecting air for agitating the electrolytic solution held between the both electrodes is provided beneath the gap between the above anodes.
U.S. Pat. No. 2,865,830 discloses an apparatus in which a electrolytic solution feeding pipe formed with a large number of holes capable of flowing out the solution is provided at the gap between the above mentioned anodes, and the electrolytic solution is ejected from said solution feeding pipe to the space defined between the both electrodes.
U.S. Pat. No. 1,969,054 discloses an apparatus in which a plurality of holes are formed through an arcuately shaped anode provided substantially horizontally around a cathode drum over about 40.degree., an electrolytic solution ejected from these holes are so made as to turn to a jet stream colliding against the cathode surface through a layer of the electrolytic solution that flows in the space between the both electrodes and along them, and dams for overflow and underflow are provided on the outlet side of the electrolytic solution to keep constant the liquid level of the electrolytic solution at the outlet side, so that the space between the both electrodes can be filled with the solution to keep a steady flow.
U.S. Pat. No. 3,151,048 further discloses an apparatus in which a plurality of pure copper bars is set up as anodes in face of the operative surface of a cathode drum, and a plurality of perforated agitator pipes is horizontally provided in the lateral direction in the space between the both electrodes, whereby the electrolytic solution in an electrolytic tank is injected into said agitator pipes by means of a pump and vertically ejected to the cathode drum surface from the holes formed on said agitator pipes.
British Patent No. 1,117,642 also discloses an apparatus in which an electrolytic solution is fed to perforated pipes provided beneath the gap between anodes, and caused to be injected from the holes into the space between both electrodes and then overflows from an open end at the upper part of said space.
As stated in the above, any of the conventionally known methods for making electrolytic metal foil and apparatus used therefor are of the type in which the electrolytic solution fed to the space between the both electrodes rises from the lower part to the upper part in said space to overflow from an upper open end.
However, the conventional methods of this type may inevitably be accompanied with a disadvantageous problem as stated below. Namely, the problem is that there is a limitation in the operation in which the flow velocity of the electrolytic solution to be allowed to flow into said space is made larger in order to refresh as highly as possible the electrolytic solution present at the space between the both electrodes. In order to make larger the flow velocity of the electrolytic solution at said space, the electrolytic solution may be injected in a large quantity and under a large pressure. However, if the pressure is made overly large, the electrolytic solution may be blown up from the upper open end of said space, causing the situation such that the solution blown up falls upon the surface of the cathode drum in scattered particles, or a mist is formed owing to gas generated by the electrolysis and may fly to impair the work environment.
For this reason, the flow velocity of the electrolytic solution must be limited to the extent that the above undesirable situation may not be caused. In the case when the flow velocity of the electrolytic solution to be fed to the space between the both electrodes is limited, the electrolytic solution present in said space can not be said to be in a refreshed state, also is in the state in which it contains a large quantity of generated gas. As a result, since the substantial density of copper ions fed to an electrolytic part is not sufficient, it is impossible to use a large current density. Moreover, the copper foil to be formed may not have sufficiently favorable physical properties and surface states, further resulting in the disadvantage that the electric power consumption may be increased because of the large electric resistance of the solution caused by the presence of generated gas.